1. Field of the Invention
The present invention generally relates to the operation of a coordinate measuring machine (CMM) and the like. More particularly, the present invention relates to a technique for providing immediate feedback to the CMM operator as to the status of the active probe tip of the machine.
2. Description of the Prior Art
Coordinate measuring machines (CMMs) have been used for years for industrial quality control to inspect the products of computer numerical control (CNC) machine tools and to check feature locations of parts after machining. Although the CMM was once considered an exotic tool found only in large manufacturing plants, the increased need for accurate measurement of components has become an important concern for small job shops as well. Accordingly, modern CMMs are significantly smaller and more affordable, and are becoming commonplace in the average machine shop.
However, in the past, the calibration and operation of a coordinate measuring machine was a slow and tedious process, typically designed to be used by skilled quality control inspectors. Even today, most CMMs are designed to be operated by a single, skilled user, typically for measuring either a single type of part or a series of the same type of parts. The CMM operator often uses a predetermined or "canned" part program in the "Run Mode" of operation to check tolerances on a production run of identical parts. More sophisticated CMM operators can create the part programs to perform simple measurements and provide basic inspection reports. That is not the case, however, for the machinist in the small job shop who only occasionally needs to use a CMM. In many of the smaller shops, these "walk-up users" are trained CNC machine tool operators, toolmakers, etc., who only need to make a few quick measurements to verify a tool setup. The walk-up user does not have extensive training in the operation of the CMM, and may have little or no familiarity with the setup or calibration procedure of the machine. Hence, the walk-up user requires a simple, fast, user-friendly computer interface that will allow him to quickly make his measurements and get back to machining the part.
Most CMMs nowadays have a fairly sophisticated computer software user interface designed for the average, skilled CMM operator. Since the CMM operator needs to know the relative position of the probe tip with respect to the axis of the machine, most software interfaces require the CMM operator to define the part's orientation with respect to the CMM, calibrate the machine to the required probe tip, and then perform the measurement. Although this procedure may suffice for the typical CMM operator who only has to set up the machine once for a certain production run, it is not very desirable when it comes to the walk-up user.
This initial setup and calibration procedure becomes even more tiresome when there are other walk-up users sharing the same CMM. In this case, each walk-up user must know what the status of the machine is before beginning to use it. Since different types of CMM probes are used to measure different parts or part features, the walk-up user must know which probe is currently on the machine and was previously calibrated before he starts to use the CMM. Unlike the case for a CMM having a single, dedicated user, the walk-up user cannot rely on a previous calibration. For example, if there were five walk-up users sharing a single CMM, they may all have their favorite probe tips calibrated for the part they are working on. When the next operator walks up to the CMM, he must check to see if the probe was modified, i.e., whether the CMM control software knows what probe is currently being used.
In fact, as can be appreciated by those skilled in the art, each CMM probe may have a different probe head, probe stylus, and probe tip orientation. For example, the commonly used star probe may have five different probe tips, but only one of the tips, called the "active probe tip", has the proper tip coordinates that correspond to those to which the CMM software was setup and calibrated. Some CMM software interfaces simply display the operator's coined name of the probe and assume that the operator has some type of probe management scheme which is consistent between multiple operators. This is often not the case. A second operator may recalibrate a different probe tip using the same coined name. For example, the first operator may pick a certain probe tip and calibrate the tip as "tip zero". The second operator could walk up to the machine, see that the software interface shows that "tip zero" has just been calibrated as he left it a short while ago, and would start using the machine. It is also possible that the walk-up user would not notice that the orientation of the probe tip had been changed by the prior operator, even with the same probe. Significant measurement errors would be introduced by the unwary operator who used CMM data taken with the wrong probe or probe tip orientation.
A need, therefore, exists for a more user-friendly and less error-prone software interface for a coordinate measuring machine which improves the operator's ability to determine the probe status of the CMM.